Drive-trains with automated transmissions are known, that use interlocking shifting elements with which, however, only shifts with traction force interruption are possible. In addition drive-trains with powershift transmissions such as dual-clutch transmissions and automatic transmissions are known, in which frictional shifting elements are used in order to carry out shifts while maintaining the traction force.
For example, from the document DE 199 17 724 A1 a drive-train for a motor vehicle is known. The drive-train comprises an electric motor and a two-gear transmission that comprises two loose wheels mounted to rotate on a shaft and which can be engaged by two associated disk clutches in order to transmit torque at an intermediate axle differential to the drive input of the vehicle.
In powershift transmissions, for safety reasons frictional shifting elements are designed as disk clutches that are held open, or ‘normally open’, i.e. which open under spring force so that if the actuating system fails the blocking of the transmission due to two simultaneously engaged gears is prevented. On the other hand, this means that a shifting element of this type has to be permanently kept in its engaged condition by an actuator. Since the clutch rotates, the transmission of rotation for example by virtue of axial bearings or hydraulic rotary ducts is necessary. However, such rotary transmissions give rise to losses that are responsible for substantial efficiency losses, particularly in the case of electric drives.